1. Field of Invention
The present invention relates to amorphous magnesium alloy having high specific strength and the method for producing the same.
2. Description of Related Arts
Crystalline magnesium alloy exhibits a high specific strength and hence can attain weight reduction of automobiles parts, which leads to savings in fuel. Representative crystalline magnesium alloys are based on Mg-Mn, Mg-Al, Mg-Zn, and Mgrare earth elements. The representative properties are 19.about.23kg/mm.sup.2 of tensile strength and 10.about.13 of specific strength for the Mg-2wt %Mn alloy and 16.about.18kg/mm.sup.2 of tensile strength and 10.about.12 of specific strength for Mg-2.about.3.5wt % Zn-0.5wt % Zr-2.5.about.4.5wt % R.E. (rare earth element) alloy.
The application development of the magnesium alloy is not as advanced as that of aluminum alloys which have already been employed for weight reduction of automobile parts, because the price of magnesium alloy is high, the specific weight is low, and further there is a problem with corrosion in ambient air.
It is known that aluminum-alloy, which is one of the light alloys, enhances strength, by vitrification, thus leading to further enhancement of the specific strength as compared with crystalline alloys. One example of an amorphous aluminum alloy is Al-R.E.-transition element alloy, whose tensile strength amounts to 100kg/mm.sup.2.
It is known that the composition of magnesium alloys which can be vitrified are limited to Mg-Al-Ag and Mg-R.E.-transition metal. However, the former amorphous Mg-Al-Ag alloy has a low crystallizing temperature and hence low heat resistance. In addition, this alloy embrittles after production and shelving at room temperature in ambient air. The latter Mg-R.E.-transition metal alloy is such a brittle material that it is destroyed by bending at room temperature in most cases.
Since the specific weight of magnesium is 1.7, which is lower than that of aluminum (2.7), when any amorphous magnesium alloy attains tensile strength of 50kg/mm.sup.2 or more, and incurs neither post-heating embrittlement due to heating at high temperature nor transformation from an amorphous state to crystals during holding at normal temperature, the so-provided amorphous magnesium alloy could be used, in practice, for light-weight parts.
Conventionally, the amorphous alloys have been produced by a single-roll apparatus for melt-quenching, which can impart a cooling speed of 10.sup.4 K/sec or more and which can provide a thickness of from 10 to 301.mu.m and width of 100 mm. Amorphous alloys with a wider area are produced by the gas-phase deposition method. Their thickness is a few micro meters. The amorphous alloys produced by these method are very thin. In order to produce thicker or bulky amorphous alloys, a ribbon produced by the single-roll method is mechanically crushed and then the crushed powder is hot-consolidated by means of, for example, extrusion and pressing. Alternatively, the amorphous powder produced by gas atomizing is consolidated by explosion bonding. However, it is difficult to produce bulky amorphous materials with 100% of amorphous structure by these methods, because the pressing and forming conditions for holding the amorphous structure are strict. In addition, since the extrusion, pressing and the like must be carried out at a temperature less than the crystallizing temperature, the required forming force is so great, that the production cost becomes impractically high.